P766: ELTROMBOPAG EFFECTIVELY ALLEVIATES APLASTIC ANEMIA THROUGH REDUCING AKT PROTEIN STABILITY AND MODULATING T LYMPHOCYTE SUBSETS
Authors: Zenghua Lin, Hui Jia, Wei Sun, Wen LI, Zhipeng Zhang, Laigen Tong, Hong Liu
Journal: HemaSphere (2023)

Topic: 11. Bone marrow failure syndromes incl. PNH - Biology & Translational Research Background: Aplastic anemia (AA) is a typical human bone marrow failure syndrome, which is due to immune attack of hematopoietic stem and progenitor cells (HSPCs) by auto-reactive T cells for most patients. Epag（eltrombopag） is a novel thrombopoietin receptor (TPO-R) agonist that has been suggested in many studies to promote hematopoiesis, alleviating the low blood platelet counts with chronic immune thrombocytopenia, possibly by the following mechanisms: stimulation of hematopoietic stem progenitor cell proliferation; promoting a more tolerizing environment via an increase in regulatory T and B cells; modulating immunity by a decreased release of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) and a increased release of transforming growth factor-β (TGF-β); mobilizing intracellular iron, resulting in a decrease in total iron burden. Aims: Studies have shown that Epag can improve the early response to IST treatment, shorten the time period of pancytopenia, and reduce side effects, which makes Epag converted from second-line therapy to first-line therapy. However, because of the slow onset of Epag, the need for long-term maintenance therapy, and the limited efficacy of monotherapy, further exploration of its mechanism is warranted, resulting in a extensive clinical application. Methods: In order to further clarify the mechanism of Epag in the treatment of AA, we used BM failure mice and 32D cells. A new possible mechanism of Epag in the treatment of AA has been demonstrated through in vitro and in vivo trials. Results: Based on our experiments, it is significantly demonstrated that Epag has failure to restore blood counts and mononuclear cells in bone marrow and spleen of BM failure mice, mainly altering the propotion of the T lymphocyte subsets (such as CD4+T, CD8+T, Treg cells) and CD8+/CD4+T ratio. Our data revealed that Epag had inhibitory effect on the proliferation and induced effect the apoptosis of wild type 32D cells induced by IFN-γ in a concentration-dependent manner. Interstingly, in IFN-γ-induced 32D cells with hTPO receptor overexpression, Epag had no obvious effect on cell apoptosis. This shows that hTPO receptor plays a key role in the function of Epag treatment. To further reveal the mechanism of Epag effect, the stability and ubiquitination of Akt protein were performed. Our results demonstrated that Epag significantly decreased the stability of Akt protein via the proteasome pathway, ultimately resulting in the inhibition of cell growth and proliferation in AA mice. Summary/Conclusion: In summary, the regulation of hematopoiesis by Epag is a complex network structure, with distinct positive and negative regulation in different species and at different times. Epag lacks the promotion of hematopoiesis through the TPO-R dependent pathway, and also further activated the cytotoxic T cells of BM failure mice. Keywords: T cell, Akt, Anemia